The objective of this research is to uncover the midbrain and medullary mechanisms which mediate binaural signals. We are proposing an 80% effort for in vivo studies of the medial superior olive (MSO) and the inferior colliculus of the kangaroo rat. For the studies on MSO nucleus, we will use low frequency masking-level-difference sound configurations as stimuli in order to differentiate the properties of excitatory-excitatory (EE) and excitatory-inhibitory (EI) binaural neurons. The MLD stimuli are narrow band noise used both as signal and masker because combinations of these stimuli provide controlled level and time differences at the ears. The objective of the collicular studies is to establish whether neurons located in this structure are sensitive to high frequency envelope time differences. The stimuli we will use in these studies have various rates of envelope amplitude modulation and depth of the modulation. The stimuli we will use in the MSO and colliculus studies have been shown to affect detection and lateralization in human psychophysical tasks. The objective of the in vitro studies is to assess the excitatory-excitatory and the excitatory-inhibitory interactions on MSO neurons with controlled electrical stimulation and to determine the time course of excitatory postsynaptic potentials and inhibitory postsynaptic potentials. A comparison of findings from the in vivo and in vitro studies will provide a basis for understanding the complex mechanisms of medullary binaural interactions.